System for binaural transmission of sound



Nov. 30 1926.

R. K. POTTER SYSTEM FOR BINAURAL TRANSMISSION OF SQUNDV Filed Dec. 31 1925 Phase Sig/Zen;

Recez'uzhy Jtaabn/ Pansmita'my Jtau'o/a/ INVENTOR flEPOWI T A TTORNE Y Patented Nev. 30,1926.

u lTEofsTArEs mun xQ-ro'r'rnn, or NEW YORK, 11. Y.,

H, 1,608,566 PATENT 1 OFFICE.

ASSIGNOR ,ro AMERICAN mamas AND TELEGRAPH COMPANY, ACOBPORATION OF NEW YORK;

srs'rnm non rumour.

'rna'nsmrssron or sounn.

Application fl a December a1, 1925'. Serial no. 7am."-

' v This invention relates to high frequency signaling systems, and particularly to a sys- .tem of the binaural type b means of which it is possible to ive to a llsteneran idea of the position of t e source of soundproducing the transmitted signal. :In a system for the. dissemination of s eech, music orother sounds such as a ra-- dro broadcast or a wire distributingsystem, it isdesirable to create within the istener a sense of the position from which the sound emanates; for example, it is particularly satisfying to be able to follow' the moyements of participants during the broadcasting of a play or to know the source of mdrvidual elements entering into the orchestration of a musical selection.

Thisinvention resides in a high frequency transmission system which maybe elther of the radio broadcast or the wire distributing type which is adapted to give to the listener;

.at thereceiving station a sense of the rela-.

.tive position of the sound that is conveyed electrically over the transmission s stem.

The conveyance of such sense 0 requires the transmission of two signals practically identical when se arat'ely con-..

sidered' but containing a smal phase and pamplitude difi'erence such as is necessary to' produce the same position discrimination as is afforded by the direct transmission of sound to the ears. The electrical circuit mustthereforebe capable of conveying these relations with a perfect balance of phase and amplitude,. because if one channel of transmission is distorted in somewhat different manner from the other the result is somewhat negatived.

This invention W1 from the following description when'read in connection with the attached drawing of which Figure 1 shows schematically a form of embodiment of the invention and Figs. 2,

3 and 4 serve to make clear the description of the principle of operation of the invention.

.In Fig. 1 the transmitting stationcomprises the microphones P and P which are separated preferably by a distance'equal to the distance between the ears of the average person. A-barrier' such as 1 may also e inserted between the microphones inv order to further simulate the separation existing between the ears 'of human beings. Micro- 7 phone P is connected by the circuit'2 with ll be clearly understoodthe primary windin of the transformer 3,

with the input circuit of the modulator M ThlS modulator may be of an 'well. known type. In the form shown int e drawing it which has itssecon ary winding connected ofthe modulator M Also connected with this input side through the transformer 13 isa source of oscillations 6, the connection including the phase shift PS The outuput side of the modulator M 's connectedby g lt-he transformer 12 with the circuit.9, whi h positionjtasconnected through the amplifier 22 with 'i the antenna T In order to carry out this invention, the modulators M and M should be of the type that effects the transmission notonly of the sidebands but also of the carrier frequency oscillations themselves. is The receiving station comprises the antenna R which is connected by means of the input circuit 14- with" the detectors D and D through the transformers 15 and 16. The output sides of these detectors are connected by the transformers 18 and 20 with the receivers 19 and 21, respectively. Bridged across thereceiving circuitat the points 23 is a branclicircuit comprising an amplifier 24, a filter 25 adapted to-transmit therethroughthe carrier frequency. and to. suppress the side bands. ;-The output side of this filter is connected with the input side of the detectors D and D A phase shifter PS is connected between thefilter 25 and the detector D and in like manner the phase shifter PS is connected withthe input side of the detector D The manner in which this. circuit func tions in order to "attain vention is as followsi a Sound emanating from a source (as indi cated by astar)' in the vicinity of the microphones, P and P will affect these devices so the objects of the inas to produce variations in the currents in tionships of the various currents are represented in Fig. 2 where C represents the oscillations applied to M and S and S repr e-' sent the side bands of that carrier. Similar- 1y C represents the carrier applied to M and S and S represent the side bands of that carrier. Both carriers and side bands will be transmitted and will be received by the receiving antenna R The currents in this antenna at any instant are substantially shown by Fig. 2, and comprise two sets of side bandsand the resultant carrier 0,. These currents will be impressed upon the input circuit 14 and in turn upon the detectors D and D A portion of the oscillations of the carrier frequency will be amplified by 24 and selected by the filter 25, and will be impressed upon the input circuits of the detectors D and D through the hase shifters PS and PS respectively. It is desirable to make clear that both sets of side bands are present in the input circuits of both detectors, and if the resultant carrier 0, alone were applied to the input circuits of the detectors it would serve to detect the signal carried by both sets of side bands in each detector. This is so because as shown in Fig. 2 the resultant carrier is not 90 degrees out of phase with the symmetrical mean of either set of side bands. For that reason it has a component in phase with the symmetrical mean of each side band which would serve to detect both sets of side bands and this would result in the loss of the binaural effect in the receivers 19 and 21. For that reason it becomes necessary to derive from the resultant carrier secondary carriers of the Same frequency but differing in phase from the resultant carrier so that it will be possible to combine the resultant carrier with each secondary carrier to produce carriers which are in phase with the symmetrical mean of one set of side bands, and degrees out of phase with the mean of the other set of bands. This desirable result is attained in the following manner: The resultant carrier O is impressed with the side bands upon the input sides of the detectors D and D At the same time a carrier of the same frequency will be impressed upon the input circuits of these detectors but will be shifted in phase by the phase shifters. To be specific, a portion of the resultant carrier which is selected by the filter 25 will be.

shifted in phase by PS to the degree'represented by 0 and the carrier frequency thus produced, which is designated C in Fig. 3, will be impressed upon the input side of detector D The angle 0 is of such magnitude that the resultant of C, and C which is represented by C in Fig. 3, is in phase with the. symmetrical mean of the side bands L 1 and 8,. It will accordingly detect the signal impressed upon the side bandsS, and S which detected signal will be impressed upon the receiver 19. Since, however, the carrier C is 90 degrees out of phase with the symmetrical mean of the side bands S and S it will not detect the signal borne by these side bands. The phase shifter PS, is adjusted to produce a'carrier such as is repret ll sented b C in Fi 4 which carrier makes an angle 0 with the resultant carrier (1,. The resultant of C, and C,, designated C's is in phase with the symmetrical mean of S, and S',, and therefore will detect the signal upon these side bands but will not detect the signal upon S and S inasmuch as it is 90 degrees out of phase with the symmetrical mean of the latter bands. The signal resulting from the detection of D will bc impressed upon the receiver 21 and the. listener will be enabled to determine the relative position of the source of sound in the vicinity of the microphones P and P by the rfcct produced upon his sense of hearing by the sound in the receivers 19 and 21.

The amplifier 24, which is preferably a unilateral device such as a vacuum tube, serves to prevent reaction between the detectors and the input circuit extending from the antenna R to the said detectors.

While this invention has been disclosed as embodied in a particular form, it is capable of embodiment in other and different forms without departing Irom the spirit and scope of the appended claims.

What is claimed is:

1. In a system for the binaural transmission of signals, the combination with a transmitting station, of a receiving station, a transmitting medium connecting the said stations, the transmitting station comprising two branch circuits, each having a transmitter and a modulator adapted to transmit side bands and carrier oscillations, of a source of carrier oscillations common to both circuit having two branch circuits connected in parallel therewith, each having a transmitter and a modulator of the carrier transmitting type, a source of carrier oscillations connected withboth modulators, one of the connections including a phase shifter adjusted to render the oscillations applied to one modulator 90 out of phase with the oscillations applied to the other modulator, of a receiving station comprising a receiving circuit having two branches connected in parallel therewithfeach branch having a detector and a receiver, and a frequency se lective circuit responsive to the carrier frequency bridged across the said receiving circuit to filter out a portion of the carrier frequency, the said frequency selective circuit having branches connecting wlth each detector, each branch having a phase shifter therein to control the phase angle of the selected carrier frequency with respect to the resultant carrier impressed by the receiving circuit upon each detector.

3. In a system for the binaural transmis sion of signals, the combination with a transmitting station having means to separately modulate carrier oscillations by the signal variations resulting from the same sound, the carrier oscillations being of the same frequency but differing in phase by 90, of a receiving station having means to receive the resultant carrier andboth sets of side bands, means to produce from the resultant carrier secondary carriers of the same frequency but displaced in phase from the resultant carrier, means to separately beat the resultant carrier and sets of side bands with each of the'secondary carriers,

and separate receivers for eachaudio-signal' resulting from such detection.

4. In a system'for the binaural transmission of signals, the combination with a transmitting station having means to separately modulate carrier oscillations by the signal variations resulting from the same sound, the carrier oscillations being of the 1 same frequency but differing in phase by 90, of a receiving station having means to receive the resultant carrier and both sets of side bands, means to produce from the resultant carrier secondary carriers of the same frequency but displaced in phase from the resultant carrier and from each other,

means to amplify the said secondary carrier, 7

means to separately beat the resultant carrier and side bands with each of the secondary carriers as amplified, and separate receivers for each audio-signal resulting from such detection.

5. In a system for the binaural transmission of signals, the method which consists in the modulation of a carrier by electrical variations resulting from sound waves, and

separately modulating by another set of electrical variations resulting from the same sound waves carrier oscillations of the same fre uency as employed in the first mentioned 10 ulation operation but differing in phase y sets of side bands and the resultant of both carriers.

6. In a system for the binaural transmission of signals, the method which consists in the modulation of a carrier by electrical variations resulting from sound waves, .separately modulating by another set of electrical variations resulting from the same sound Waves oscillations of the same frequency as employed in thefirst mentioned modulation operation but differing in phase 90 therefrom, and transmitting both by 90 therefrom, selecting at a receiving station a portion of the' said carrier, changcarrier on a second detector together with the side bands and the resultant carrier, and receiving the resultant audio frequency signals from both detecting operations.

7. In a system for the binaural transmission of signals, the combination with a transmitting station having means to produce two sets of side bands, based upon carriers of the same frequency and differing in phase by 90? of a receiving system having means'to produce carriers from the transmitted carrier, the said produced carriers being in phase with the mean of each set of side bands.

In testimony whereof, I have signed my name to this specification this 30th day of December, 1925. 4 RALPH K. POTTER.

ing the phase of a portion of the selected ll l 

